Now a days people are more focused on social marketing.
They wants to make their social profiles and pages more and more popular.
They want more and more likes and followers for their social presenceses.
So one of the way to get popularity is promoting this kind of profiles and pages on your popular pages.
By promoting it they gets more popularity for their pages and you can ask for money of promotion. Because you know that there is no free lunch in this world.
Same way you can promote products for eCommerce company by doing that companies gets more visitors and you know that more visitors means more selling and after all more money.
You can promote articles, product reviews as well.